Article coated with baked layer of water-soluble heat-resistant insulating varnish

ABSTRACT

A coated article comprising a metal support and a baked layer of a water soluble heat-resistant insulating varnish containing a resin comprising ester groups and imide rings in the molecule dissolved in water using a volatilizable basic compound, the resin comprising the reaction product of 
     (A) a carboxyl-containing polyesterimide resin having an acid value of about 30 to 150 obtained by reacting (a) a polyhydric alcohol component comprising at least one organic polyhydric alcohol and containing about 10 to 60 mol % of an imide ring-containing glycol of the general formula (I): ##STR1## wherein R 1  is a trivalent aromatic group, R 2  is a divalent organic group, and n is an integer of 1 to 3, with (b) a polycarboxylic acid component comprising at least one trivalent or divalent organic carboxylic acid or the anhydride thereof, where about 30 to 100 mol % of which comprises an aromatic tricarboxylic acid or the anhydride thereof so that the equivalent ratio (OH/COOH) between the polyhydric alcohol component and the polycarboxylic acid component is about 1.0 to 2.0; 
     (B) 1,2,3,4-butanetetracarboxylic acid or an imide-forming derivative thereof; and 
     (C) an organic diamine.

The present application is a divisional application of U.S. Ser. No.617,135, filed Sept. 26, 1975, now U.S. Pat. No. 4,101,488.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to water-soluble heat-resistant insulatingvarnishes.

2. Description of the Prior Art

Most of the conventional insulating varnishes, above all, wire enamels,are of the solvent-based type dissolved in an organic solvent such ascresol, xylene or naphtha. These varnishes, however, have involved highproduction costs because the solvent volatilizes during the productionof insulated electric wires and cables and it is also necessary toincinerate the solvent completely using a burning furnace. The use ofthese organic solvents also is likely to cause air pollution, andbecause of the offensive odor of the organic solvent, the workingenvironment is not entirely satisfactory. In addition, there is always adanger of fire because of the flammability of the solvent. It hastherefore been desired to develop insulating varnishes which havereduced likelihood of causing these hazards.

In recent years, there has been a rapidly increasing demand forpolyesterimide resin varnishes as cable and wire enamels because oftheir superior heat resistance. However, films obtained from these resinvarnishes have the serious defect that when stretched 3 to 5%, theydevelop a marked crazing phenomenon in a solvent or water, andtherefore, it has been strongly desired to solve the problem of crazingfor practical purposes.

SUMMARY OF THE INVENTION

An object of this invention is to provide a water-soluble heat-resistantinsulating varnish free from the defects of conventional insulatingvarnishes.

Extensive investigations have led to the discovery that the above objectof this invention is achieved with a varnish comprising a resincontaining ester groups and imide rings in the molecule dissolved inwater using a basic compound, the resin comprising the reaction productof

(A) a carboxyl-containing polyesterimide resin having an acid value ofabout 30 to 150 obtained by reacting (a) a polyhydric alcohol componentcomprising at least one organic polyhydric alcohol and containing about10 to 60 mol % of an imide ring-containing glycol of the general formula(I): ##STR2## wherein R₁ is a trivalent aromatic group, R₂ is a divalentorganic group, and n is an integer of 1 to 3, and (b) a polycarboxylicacid component comprising at least one trivalent or divalent organiccarboxylic acid or the anhydride thereof, about 30 to 100 mol % of whichcomprises an aromatic tricarboxylic acid or the anhydride thereof sothat the equivalent ratio (OH/COOH) between the polyhydric alcoholcomponent and the polycarboxylic acid component is about 1.0 to 2.0;

(B) 1,2,3,4-butanetetracarboxylic acid or an imideforming derivativethereof; and

(C) at least one organic diamine.

DETAILED DESCRIPTION OF THE INVENTION

The water-soluble heat-resistant insulating varnish obtained inaccordance with this invention contains water as a medium, and does notrequire an expensive solvent. As further advantages, this varnish isodorless and non-toxic and is free from the danger of fire or explosion.Moreover, it is surprising that a crazing phenomenon, which is thedefect of conventional ester imide resins, does not occur with thisvarnish. This advantage is most important in practical applications ofthe varnish, and constitutes a characteristic feature of this invention.

The imide ring-containing glycol used in the polyhydric alcoholcomponent in this invention is expressed by the general formula (I):##STR3## wherein R₁, R₂ and n are the same as defined above, and can beprepared by reacting an aromatic tricarboxylic anhydride of the generalformula (II): ##STR4## wherein R₁ is a trivalent aromatic group, with anorganic diamine of the general formula (III):

    H.sub.2 N--R.sub.2 --NH.sub.2                              (III)

wherein R₂ is a divalent organic group, at a temperature from about 150°C. to about 300° C. in a glycol selected from the group consisting ofethylene glycol, diethylene glycol and triethylene glycol, with theamount of the aromatic tricarboxylic anhydride being adjusted to about 2mols per mol of the organic diamine of the general formula (III). Thepresence of materials remaining unreacted is not preferred. The reactioncan be carried out by feeding the aromatic tricarboxylic anhydride, theorganic diamine and the glycol simultaneously to the reaction vessel andgradually elevating the temperature of the resulting mixture from roomtemperature to about 150° C. followed by allowing the mixture to reactat a temperature of about 150° to about 300° C., preferably 150° to 200°C., for several hours to obtain a resinous material. Generally, thereaction does not require catalysts, an inert atmosphere or pressurizedconditions. The use of a watersoluble solvent in this reaction is ofteneffective for rendering the reaction system homogeneous. Examples ofpreferred solvents are organic polar solvents such asN,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide,N,N-diethylacetamide or N-methyl-2-pyrrolidone. Sometimes, solvents ofthe cellosolve or carbitol type can also be used. The amount of thesolvent is an amount sufficient to render the reaction systemhomogeneous. The solvent can be removed after the formation of the imidering-containing glycol of the general formula (I), or can be left in thewater-soluble heat-resistant insulating varnish finally obtained. Theresulting imide ring-containing glycol of the formula (I) can be usedafter purification, or usually, can be used as a raw material in thesubsequent reaction step without purification.

The aromatic tricarboxylic anhydride used to prepare the imidering-containing glycol of the general formula (I) is selected from thoseof the above general formula (II) in which R₁ is selected from the groupconsisting of ##STR5## wherein R₃ is selected from the group consistingof ##STR6##

Typical examples of aromatic tricarboxylic anhydrides of the generalformula (II) are trimellitic anhydride, hemimellitic anhydride, 3,4,3'(or 3,4,4')-diphenyltricarboxylic anhydride, 3,4,3' (or3,4,4')-diphenylmethanetricarboxylic anhydride, 3,4,3' (or3,4,4')-diphenylethertricarboxylic anhydride, 3,4,3' (or3,4,4')-diphenylsulfidetricarboxylic anhydride, 3,4,3' (or3,4,4')-diphenylsulfonetricarboxylic anhydride, 3,4,3' (or3,4,4')-diphenylketonetricarboxylic anhydride, 3,4,3' (or3,4,4')-diphenylpropanetricarboxylic anhydride, and mixtures of theseanhydrides.

The organic diamines of the general formula (III) used to obtain theabove imide ring-containing glycol of the general formula (I) areselected from those of the above general formula (III) in which R₂ isselected from the group consisting of

    --CH.sub.2).sub.n.sbsb.1

wherein n₁ is an integer of 1 to 6, ##STR7## wherein R'₃ is selectedfrom the group consisting of ##STR8## is selected from the groupconsisting of a hydrogen atom, an alkoxy group, an alkyl group and ahalogen atom.

Typical examples of organic diamines of the general formula (III)include ethylene diamine, hexamethylene diamine, meta-xylylene diamine,para-xylylene diamine, meta-phenylene diamine, para-phenylene diamine,benzidine, 3,3'-dimethoxybenzidine, 3,3'-dichlorobenzidine,3,3'-dimethylbenzidine, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene,4,4'-diaminodiphenylmethane, 4,4' (or 3,4')-diaminodiphenyl ether,4,4'-diaminodiphenyl sulfide, 3,3' (or 4,4')-diaminodiphenyl sulfone,4,4'-diaminodiphenyl ketone, 4,4'-diaminodiphenyl propane,3,4'-diaminobenzanilide, and mixtures of these organic diamines.

Examples of organic polyhydric alcohols which can be used in combinationwith the imide ring-containing glycol of the general formula (I) in thepolyhydric alcohol component include ethylene glycol, propylene glycol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethylene glycol,dipropylene glycol, triethylene glycol, 4,4'-dihydroxymethyldiphenyl,4,4'-dihydroxyethyldiphenyl, 4,4'-dihydroxymethyldiphenylmethane,4,4'-dihydroxyethyldiphenylmethane, 4,4'-dihydroxymethyldiphenyl ether,4,4'-dihydroxyethyldiphenyl ether, 4,4'-dihydroxymethyldiphenyl sulfide,4,4'-dihydroxyethyldiphenyl sulfide, 4,4'-dihydroxymethyldiphenylsulfone, 4,4'-dihydroxyethyldiphenyl sulfone,4,4'-dihydroxymethyldiphenyl ketone, 4,4'-dihydroxyethyldiphenyl ketone,4,4'-dihydroxymethyldiphenylpropane, 4,4'-dihydroxyethyldiphenylpropane,bis-(2-hydroxyethyl)terephthalate, bis-(2-hydroxyethyl isophthalate,bis-(2-hydroxyethyl)phthalate, glycerol, trimethylol propane,1,2,6-hexanetriol, 3-methyl-1,3,5-hexanetriol,tris-(2-hydroxyethyl)isocyanurate, pentaerythritol, and mixtures ofthese organic polyhydric alcohols.

The imide ring-containing glycol of the general formula (I) is used inthe polyhydric alcohol component generally in an amount of about 10 to60 mol % based on the total mols of the imide ring-containing glycol ofthe general formula (I), and the organic polyhydric alcohol in thepolyhydric alcohol component. If the amount is less than about 10 mol%,a baked film of the water-soluble heat-resistant insulating varnishfinally obtained has poor thermal properties. If the amount is largerthan about 60 mol%, the resulting water-soluble heat-resistantinsulating varnish sometimes becomes turbid.

The aromatic tricarboxylic acid or anhydride thereof used in thepolycarboxylic acid component in this invention is represented by thegeneral formula (IV) or (V), respectively ##STR9## wherein R₁ is atrivalent aromatic group, in which R₁ is selected from the groupconsisting of ##STR10## wherein R₃ is selected from the group consistingof ##STR11##

Typical examples of aromatic tricarboxylic acids or anhydride thereof ofthe general formulas (IV) and (V) are trimellitic acid (or the anhydridethereof), hemimellitic acid (or the anhydride thereof), trimesic acid(or the anhydride thereof), 3,4,3' (or 3,4,4')-diphenyltricarboxylicacid (or the anhydride thereof), 3,4,3' (or3,4,4')-diphenylmethanetricarboxylic acid (or the anhydride thereof),3,4,3' (or 3,4,4')-diphenylether tricarboxylic acid (or the anhydridethereof), 3,4,3' (or 3,4,4')-diphenylsulfidetricarboxylic acid (or theanhydride thereof), 3,4,3' (or 3,4,4')-diphenylsulfonetricarboxylic acid(or the anhydride thereof), 3,4,3' (or3,4,4')-diphenylketonetricarboxylic acid (or the anhydride thereof),3,4,3' (or 3,4,4')-diphenylpropanetricarboxylic acid (or the anhydridethereof), and mixtures thereof.

The trivalent or divalent organic carboxylic acid or the anhydridethereof which can be used together with the above aromatic tricarboxylicacid or the anhydride thereof of the general formulas (IV) and (V) inthe polycarboxylic acid component is preferably an organic dicarboxylicacid or, the anhydride thereof expressed by the general formula (VI) or(VII), respectively,

    HOOC--R.sub.5 --COOH                                       (VI)

or ##STR12## in which R₅ is a divalent organic group selected from thegroup consisting of

    --CH.sub.2).sub.n.sbsb.2

in which n₂ is an integer of 1 to 8, ##STR13## in which R₃ is selectedfrom the group consisting of ##STR14##

Typical examples of the above polycarboxylic acids and anhydridesthereof of the general formulas (VI) and (VII) are succinic acid,succinic anhydride, adipic acid, malonic acid, sebacic acid, phthalicacid, phthalic anhydride, isophthalic acid, terephthalic acid,naphthalene-1,4 (or 1,5 or 2,6, etc.)-dicarboxylic acid having theformula ##STR15## 3,3' (or 4,4', etc.)-dicarboxydiphenyl having theformula ##STR16## 3,3' (or 4,4', etc.)-dicarboxydiphenylmethane, 3,3'(or 4,4', etc.)-dicarboxydiphenyl ether, 3,3' (or 4,4',etc.)-dicarboxydiphenyl sulfide, 3,3' (or 4,4', etc.)-dicarboxydiphenylsulfone, 3,3' (or 4,4', etc.)-dicarboxydiphenyl ketone, 3,3' (or 4,4',etc.)-dicarboxydiphenyl propane having the formula ##STR17## wherein Rrepresents a methylene group, an oxygen atom, a sulfur atom, an --SO₂ --group, a ##STR18## or mixtures thereof.

The 1,2,3,4-butanetetracarboxylic acid and the imide-forming derivativesthereof (B) are compounds capable of forming an imide ring by reactionwith an organic diamine, such as 1,2,3,4-butanetetracarboxylic acid,1,2,3,4-butanetetracarboxylic monoanhydride,1,2,3,4-butanetetracarboxylic dianhydride, or dimethyl1,2,3,4-butanetetracarboxylate.

As (C) the organic diamine to be reacted with (B) the1,2,3,4-butanetetracarboxylic acid (or an imide-forming derivativethereof), the organic diamine of the formula (III):

    H.sub.2 N--R.sub.2 --NH.sub.2                              (III)

wherein R₂ is a divalent organic group, as herein before described,which is used in the preparation of the imide ring-containing glycol ofthe general formula (I), can be advantageously utilized.

The water-soluble heat-resistant insulating varnish of this inventioncan be prepared by the following procedure.

First, the polyhydric alcohol component comprising the organicpolyhydric alcohol containing about 10 to 60 mol% of the imidering-containing glycol of the general formula (I) is reacted with thepolycarboxylic acid component comprising the trivalent or divalentorganic carboxylic acid of the general formula (VI) (or the anhydridethereof of the general formula (VII)), where about 30 to 100 mol% ofwhich is the aromatic tricarboxylic acid of the general formula (IV) (orthe anhydride thereof of the general formula (V)), with the polyhydricalcohol component being used in excess, to obtain thecarboxyl-containing polyesterimide resin (A). In this polycondensationreaction, a suitable equivalent ratio of the polyhydric alcoholcomponent to the polycarboxylic acid component (OH/COOH) is usuallyabout 1.0 to 2.0, preferably 1.15 to 1.95. If the ratio is less thanabout 1.0, a gelation phenomenon occurs before the molecular weight ofthe carboxyl-containing polyesterimide resin (A) sufficiently increasesin the course of the reaction. On the other hand, if the ratio is above2.0, the resulting carboxyl-containing polyesterimide resin (A) has solow a molecular weight that a tough film is difficult to form at thetime of baking the resulting water-soluble heat-resistant insulatingvarnish. Ratios in excess of about 2.0 can of course be used if ameasure is taken to distill the resulting reaction mixture at reducedpressure to thereby remove the organic polyhydric alcohol from thereaction system and to increase the molecular weight of thecarboxyl-containing polyesterimide resin (A).

The amount of the aromatic tricarboxylic acid of the general formula(IV) (or the anhydride thereof of the general formula (V)) is specifiedas about 30 to 100 mol% of the polycarboxylic acid component, becauseotherwise the resultingresin has poor solubility in water, and films ofthe varnish finally obtained sometimes have a poor appearance and poorthermal or electrical properties.

The reaction temperature at this stage is about 100° to 300° C.,preferably 160° to 220° C. When the reaction is performed at thistemperature for several hours, water distills off, and the reactionmixture gradually becomes a viscous resinous product with a decrease inacid value. The reaction is stopped when the acid value of the productis about 30 to 150, preferably 50 to 120. If the acid value is less thanabout 30 as a result of this reaction, the water-soluble heat-resistantinsulating varnish finally obtained becomes turbid, and a poorappearance and poor thermal properties of the baked films tend toresult. If the acid value is higher than about 150, the amount of theresidual carboxyl groups in the baked films of the varnish isunnecessarily large, which tends to cause poor mechanical and electricalproperties of the baked films.

A suitable amount of the polyimide component in the preparation of thecarboxyl-containing polyesterimide resin (A) at this stage is usuallyabout 20 to 70% by weight, preferably 30 to 60% by weight, based on thetotal amount of the polyester component and the polyimide component.

If the content of the polyimide component is less than about 20% byweight, the baked films finally obtained sometimes have poor thermalresistance. If the content is more than about 70% by weight, the thermalproperties of the baked films are good, but unless the glycol is used ina great quantity in the preparation of the imide ring-containing glycolof the general formula (I), the reaction system solidifies, and reactionoperation becomes difficult.

The carboxyl-containing polyesterimide resin (A) so obtained is thenreacted with (B) the 1,2,3,4-butanetetracarboxylic acid (or animide-forming derivative thereof) and (C) the organic diamine to form awater-soluble heat-resistant resin. A suitable amount of thebutanetetracarboxylic acid or an imide-forming derivative thereof and(C) the organic diamine combined is about 20 to 200 parts by weight,preferably 30 to 150 parts by weight, per 100 parts by weight of thecarboxyl-containing polyesterimide resin (A). If this total amount isless than about 20 parts by weight, the resulting water-solubleheat-resistant insulating varnish has poor solubility, and sometimesbecomes turbid. Furthermore, baked films of this varnish have poorthermal resistance. On the other hand, if the total amount is more thanabout 200 parts by weight, the cost of production becomes too high forthe extent of improvement in the thermal properties of the resultingbaked films.

A suitable equivalent ratio of (B) the 1,2,3,4-butanetetracarboxylicacid (or the imide-forming derivative thereof) to (C) the organicdiamine is about 0.5 to 2, preferably 0.8 to 1.3. If the equivalentratio is less than about 0.5, the unreacted organic diamine (C) remainsin the water-soluble heat-resistant varnish finally obtained, and tendsto cause the varnish to be turbid. On the other hand, if the equivalentratio is higher than about 2.0, gelation tends to occur during thereaction.

When the reaction at this stage is performed usually at about 100° to300° C., preferably 130° to 200° C., water distills off. The mainreaction at this time is an imidization reaction between (B) the1,2,3,4-butanetetracarboxylic acid and (C) the organic diamine, butesterification occurs by the reaction of the carboxyl groups (or theanhydrides thereof) of (B) the butanetetracarboxylic acid (or theimide-forming derivative thereof) with the hydroxyl groups of thecarboxyl-containing polyesterimide resin (A) to increase the molecularweight of the resin. In some cases, amide linkages can be formed by thereaction of the amino groups with the carboxyl groups of thecarboxyl-containing polyesterimide resin (A). When the reaction isstopped while the acid value of the reaction product is within the rangeof about 30 to 150, a reddish-brown transparent resin is obtained.

At this stage, a volatilizable basic compound, such as aqueous ammonia,and water are added to the resulting resin to form a water-solubleheat-resistant insulating varnish.

The water-soluble heat-resistant insulating varnish so obtained containsmainly ester groups and imide groups in the molecule. Since the resin inthe form of a salt with the basic compound such as ammonia dissociatesat the time of baking, cross-linking proceeds within the molecule andbetween the molecules thereby to provide a film having superiorinsulating properties.

As previously stated, the reaction is stopped when the acid value of thereaction product usually becomes about 30 to 150. If the acid value isless than about 30, the resin does not become water-soluble even byaddition of a basic compound such as ammonia, and the varnish sometimesbecomes turbid. If the acid value is above about 150, unreactedmaterials remain, and when the resulting water-soluble heat-resistantinsulating varnish is baked, it is difficult to obtain a film havingsuperior mechanical and electrical properties.

The compound to be added in order to render the resin water-soluble ispreferably a basic compound volatilizable at the time of baking thewater-soluble heat-resistant insulating varnish. Typical examples ofvolatile basic compounds include ammonia, trialkylamines such astrimethylamine, triethylamine or tributylamine, N-alkyldiethanolaminessuch as N-methyldiethanolamine, N-ethyldiethanolamine orN-propyldiethanolamine, N,N-dialkylethanolamines such asN,N-dimethylethanolamine or N,N-diethylethanolamine,N,N-dibutylethanolamine, monoethanolamine, diethanolamine,triethanolamine, and mixtures thereof.

The amount of the volatilizable basic compound is an amount sufficientto render the resin water-soluble, that is, an amount sufficient toneutralize the carboxyl groups in the resin. It is not necessary toconvert all of the residual carboxyl groups into salts, and therefore,it is sufficient if the amount of the volatilizable basic compound isonly larger than that which renders the resin water-soluble. Even ifammonia or aqueous ammonia is added in excess, heating the varnish atabout 100° C. can result in the removal of the excess. The amount addedgenerally is about 0.3 to 3 equivalents based on the residual carboxylgroups in the resin.

The pH of the resulting water-soluble heat-resistant insulating varnishis usually about 5 to 9, and preferably it is adjusted to 6 to 8.

The functional characteristics of varnishes according to the presentinvention will vary to some extent depending upon starting materials andthe degree of polymerization employed, but generally the concentrationof the components contained in the aqueous solution can range from about30 to about 55% by weight (measured as solid content at 200° C.±2° C.for 2 hours) with the viscosity being in the range of about 1 to about100 poises (measured at 30° C. using a Brookfield type viscosimeter).

The water-soluble heat-resistant insulating varnish so obtained providesa film of good properties even when the solvent is solely water. It issometimes effective, however, to replace up to about 30% by weight ofthe water with a water-soluble high-boiling solvent since this rendersfilm formation easy, and provides a film having a smooth surface.Examples of suitable water-soluble high-boiling solvents are ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol monoisopropyl ether, ethylene glycol monobutyl ether, ethyleneglycol monoisobutyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monoisopropylether, diethylene glycol monobutyl ether, diethylene glycol monoisobutylether, triethylene glycol monomethyl ether, triethylene glycol monoethylether, triethylene glycol monoisopropyl ether, triethylene glycolmonobutyl ether, triethylene glycol monoisobutyl ether, ethylene glycolmonomethyl ether acetate, ethylene glycol monoethyl ether acetate,ethylene glycol, propylene glycol, diethylene glycol, dipropyleneglycol, triethylene glycol, glycerol, N,N-dimethylformamide,N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide,N-methyl-2-pyrrolidone, N,N-dimethylmethoxyacetamide,N-methylcaprolactam, and mixtures of these solvents.

Conventional solvent-based varnishes do not provide films havingsufficient properties unless an organic metal compound such astetrabutyl titanate is added as a cross-linking agent at the time ofbaking. In contrast, according to this invention, baked films ofsufficient properties can be obtained without using such a curing agent.In some cases, however, the addition of a water-soluble compound such asa water-soluble organic metal compound, a water-soluble phenolic resin,a water-soluble amino resin or a water-soluble epoxy resin as a curingagent can expedite film formation. Of the water-soluble organic metalcomponents, titanium ammonium lactate of the formula ##STR19## titaniumlactate of the formula ##STR20## and zirconium ammonium lactate of theformula ##STR21## are especially effective. The use of such awater-soluble compound is an amount of up to about 10 parts by weightper 100 parts by weight of the resin (the non-volatile component in thewater-soluble heat-resistant insulating varnish) is sufficientlyeffective. A preferred amount is 0.1 to 5.0 parts by weight per 100parts by weight of the resin.

The varnishes according to the present invention can be baked at atemperature above about 200° C., preferably 300° to 500° C.

The water-soluble heat-resistant insulating varnish of this invention isuseful for electric insulation, especially as wire enamels. It is alsouseful in such applications as flexible printed circuit substrates,panel heaters or tape cables, or coated and baked on a conductor foil.The insulating varnish of this invention can also be applied as a primeror an overcoat of other paints.

The insulating varnish obtained by this invention provides useful filmsby application to conductors using an electric method, for example,electrophoresis, followed by baking. In some cases, the insulatingvarnish of this invention can also be used for coating transportationfacilities such as vehicles, ships or airplanes, building materials suchas aluminum sashes, and household appliances such as refrigerators orwashing machines.

Alternatively, the resulting water-soluble heat-resistant insulatingvarnish can be powdered by evaporation of water, and can provide usefulcoated products using coating methods such as an electrostatic coatingmethod or a fluidized bed coating method.

Incidentally, in the preparation of the carboxyl-containingpolyesterimide resin in accordance with this invention, a part of thearomatic tricarboxylic acid of the polycarboxylic acid component reactedwith the polyhydric alcohol component comprising the organic polyhydricalcohol containing the imide ring-containing glycol of the generalformula (I) can be replaced by an aromatic tetracarboxylic acid (oranhydride thereof) in an amount of up to about 30 mol % based on theamount of the tricarboxylic acid or the anhydride thereof used.

The tetracarboxylic acid or the anhydride thereof is a compoundexpressed by the general formulas (VIII) or (IX), respectively ##STR22##wherein R₆ is a tetravalent aromatic group selected from the groupconsisting of ##STR23## wherein R₃ is selected from the group consistingof ##STR24##

Typical examples of the aromatic tetracarboxylic acid of the generalformula (VIII) or the anhydride thereof of the general formula (IX) arepyromellitic acid, pyromellitic dianhydride, 1,2,5,6 (or 1,4,5,8 or2,3,6,7)-naphthalenetetracarboxylic acid (or the dianhydride thereof),3,3',4,4'-diphenyltetracarboxylic acid (or the dianhydride thereof),3,3',4,4'-diphenylmethanetetracarboxylic acid (or the dianhydridethereof), 3,3',4,4'-diphenylethertetracarboxylic acid (or thedianhydride thereof), 3,3',4,4'-diphenylsulfidetetracarboxylic acid (orthe dianhydride thereof), 3,3',4,4'-diphenylsulfonetetracarboxylic acid(or the dianhydride thereof), 3,3',4,4'-diphenylketonetetracarboxylicacid (or the dianhydride thereof),3,3',4,4'-diphenylpropanetetracarboxylic acid (or the dianhydridethereof), and mixtures thereof.

The following Examples are given to illustrate the invention morespecifically. Unless otherwise indicated, all percents, parts, ratiosand the like are by weight.

EXAMPLE 1

A 1-liter four-necked flask equipped with a Dean-Stark trap, athermometer, a dropping funnel and a stirrer was charged with 38.4 g(0.2 mol) of trimellitic anhydride, 19.8 g (0.1 mol) of4,4-diaminodiphenylmethane and 124 g (2.0 mols) of ethylene glycol, andthe mixture was heated with stirring. At a temperature about 100° C.,the mixture became transparent, but at about 140° C., becameheterogeneous. On further heating with stirring, water began to distilloff at a temperature of about 180° C. When the mixture was reacted at180° to 195° C. for 3 hours, it became transparent. When the reactionwas performed for 2 hours at this temperature, the acid value of theproduct became zero. An infrared absorption spectroscopic analysis ofthe resulting compound showed that there was an absorption correspondingto the imide ring at 1710 cm⁻¹ and 1770 cm⁻¹. As a result of elementalanalysis, the product was found to be a compound mainly containing animide ring-containing plycol of the following formula (A): ##STR25##

Then, the temperature of the reaction system was increased to more than200° C., and 63 g of the ethylene glycol was distilled off. Thetemperature was then reduced to 150° C., and 67.2 g (0.35 mol) oftrimellitic anhydride and 16.6 g (0.1 mol) of isophthalic acid wereadded (the OH/COOH ratio was 1.41). When the reaction was performed at180° to 190° C. for 1 hour, water distilled off, and a viscous resinousproduct having an acid value of 119 was obtained. Then, the temperaturewas reduced to 130° C., and 58.5 g (0.25 mol) of1,2,3,4-butanetetracarboxylic acid and 49.5 g (0.25 mol) of4,4'-diaminodiphenylmethane were added. The reaction was performd at130° to 150° C. for 1 hour. As a result, water distilled off, and areddish-brown transparent resinous product having an acid value of 132was obtained. Then, the temperature was reduced to 110° C., and 50 g ofaqueous ammonia (concentration more than 28%; industrial grade) dilutedwith 100 g of water was added through the dropping funnel, and themixture was stirred at 100° C. for 30 minutes. The excess ammoniavolatilized, and a reddish-brown transparent water-solubleheat-resistant insulating varnish was obtained. The varnish was furtherdiluted with water to adjust the viscosity of the varnish to 15 poises(measured at 30° C. using a Brookfield-type viscometer). Thenon-volatile content of this varnish (after drying for 2 hours at200°±2° C.) was 42.5%. This varnish had a pH of 6.5.

EXAMPLE 2

A 1-liter four-necked flask equipped with a Dean-Stark trap, athermometer, a dropping funnel and a stirrer was charged with 76.8 g(0.4 mol) of trimellitic anhydride, 40.0 g (0.2 mol) of4,4'-diaminodiphenyl ether and 124 g (2.0 mols) of ethylene glycol, andthe mixture was heated with stirring. At a temperature of about 100° C.,the mixture became transparent, but became heterogeneous at about 120°C. On further heating, water began to distill off at about 180° C. Whenthe mixture was reacted at 180° to 195° C. for 5 hours, it becametransparent. When it was further reacted at this temperature for 3hours, the acid value of the reaction product became zero. As a resultof the same analysis as in Example 1, the resulting product was found tobe a compound containing mainly an imide ring-containing glycol of thefollowing formula (B): ##STR26##

Then, the temperature was increased to more than 200° C., and 46 g ofthe ethylene glycol was distilled off. The temperature was then reducedto 150° C., and 76.8 g (0.4 mol) of trimellitic anhydride was added (theOH/COOH ratio was 1.75). When the reaction was performed at 180° to 190°C. for 1 hour, water distilled off, and a viscous resinous producthaving an acid value of 108 was obtained. Then, the temperature wasreduced to 130° C., and 58.5 g (0.25 mol) of1,2,3,4-butanetetracarboxylic acid and 39.6 g (0.2 mol) of4,4'-diaminodiphenylmethane were added. When the reaction was performedat 130° to 150° C. for 1 hour, water distilled off, and a reddish-browntransparent resinous material having an acid value of 126 was obtained.Then, the temperature was reduced to 110° C., and 50 g of aqueousammonia (concentration more than 28%; industrial grade) diluted with 100g of water was added, and the mixture was stirred for 30 minutes at 100°C. The excess ammonia volatilized and a reddish-brown transparentwater-soluble heat-resistant insulating varnish was obtained. Thevarnish was further diluted with water to adjust the viscosity of thevarnish to 16 poises (measured at 30° C. using a Brookfield-typeviscometer). The non-volatile content of this varnish (after drying for2 hours at 200°±2° C.) was 43.6%. The varnish had a pH of 6.7.

EXAMPLE 3

A 1-liter four-necked flask equipped with a Dean-Stark trap, athermometer, a dropping funnel and a stirrer was charged with 115.2 g(0.6 mol) of trimellitic anhydride, 32.4 g (0.3 mol) of meta-phenylenediamine and 212 g (2.0 mols) of diethylene glycol, and the mixture washeated with stirring. At a temperature of about 100° C., the mixturebecame transparent, but became heterogeneous at a temperature of about120° C. On further heating, water began to distill off at about 180° C.When the mixture was reacted at 180° to 195° C. for 7 hours, it becametransparent. When it was further reacted at this temperature for 3hours, the acid value of the reaction product became zero. As a resultof the same analysis as in Example 1, the resulting product was found tobe a compound containing mainly an imide ring-containing glycol of thefollowing formula (C): ##STR27##

Then, the temperature was increased to 245° C., and 106 g of thediethylene glycol was distilled off. The temperature was then reduced to150° C., and 76.8 g (0.4 mol) of trimellitic anhydride was added (theOH/COOH ratio was 1.16). When the mixture was reacted at 180° to 195° C.for 0.5 hour, water distilled off, and a viscous resinous product havingan acid value of 132 was obtained. Then, the temperature was reduced to130° C., and 58.5 g (0.25 mol) of 1,2,3,4-butanetetracarboxylic acid and60.0 g (0.3 mol) of 4,4'-diaminodiphenylether were added. When themixture was reacted at 130° to 150° C. for 1 hour, water distilled off,and a reddish-brown transparent resinous product having an acid value of109 was obtained. Then, the temperature was further reduced to 110° C.,and 50 g of aqueous ammonia (concentration more than 28%; industrialgrade) diluted with 100 g of water was added. When the mixture wasstirred at 100° C. for 30 minutes, the excess ammonia volatilized, and areddish-brown transparent water-soluble heat-resistant insulatingvarnish was obtained. The varnish was diluted further with water toadjust the viscosity of the varnish (as measured at 30° C. using aBrookfield-type viscometer) of 20 poises. The non-volatile content(after drying for 2 hours at 200°±2° C.) was 44.3%. The varnish had a pHof 6.8.

EXAMPLE 4

A 1-liter four-necked flask equipped with a Dean-Stark trap, athermometer, a dropping funnel and a stirrer was charged with 76.8 g(0.4 mol) of trimellitic anhydride, 49.6 g (0.2 mol) of3,3'-diaminodiphenyl sulfone and 300 g (2.0 mols) of triethylene glycol,and the mixture was heated with stirring. At a temperature of about 100°C., it became transparent, but at about 120° C., became heterogeneous.On further heating with stirring, water began to distill off at about180° C. When the mixture was reacted at 180° to 195° C. for 5 hours, itbecame transparent. When it was reacted further at this temperature for2 hours, the acid value of the reaction product became zero. As a resultof the same analysis as in Example 1, the resulting product was found tobe a compound containing mainly an imide ring-containing glycol of theformula (D): ##STR28##

Then, 92 g of the triethylene glycol was distilled off at reducedpressure. The temperature was then reduced to 150° C., and 57.6 g (0.3mol) of trimellitic anhydride and 83.0 g (0.5 mol) of isophthalic acidwere added (the OH/COOH ratio was 1.24). When the mixture was reacted at180° to 190° C. for 2 hours, water distilled off, and a viscous resinousproduct having an acid value of 116 was obtained. The temperature wasthen reduced to 130° C., and 108 g (0.5 mol) of1,2,3,4-butanetetracarboxylic monoanhydride and 100 g (0.5 mol) of4,4'-diaminodiphenyl ether were added. When the mixture was reacted at130° to 150° C. for 1 hour, water distilled off, and a reddish-browntransparent resinous product having an acid value of 80 was obtained.The temperature was then reduced to 110° C., and 40 g of aqueous ammonia(concentration more than 28%; industrial grade) diluted with 100 g ofwater was added through the dropping funnel. When the mixture wasstirred at 100° C. for 30 minutes, the excess ammonia volatilized, and areddish-brown transparent water-soluble heat-resistant insulatingvarnish was obtained. The varnish was further diluted with water toadjust the viscosity of the varnish to 18 poises (as measured at 30° C.using Brookfield-type viscometer). The non-volatile content of thisvarnish (after drying for 2 hours at 200°±2° C.) was 39.8%. The varnishhad a pH of 6.9.

EXAMPLE 5

A compound comprising an imide ring-containing glycol of the formula (A)was prepared in the same way as in Example 1 from 76.8 g (0.4 mol) oftrimellitic anhydride, 39.6 g (0.2 mol) of 4,4'-diaminodiphenylmethaneand 124 g (2.0 mols) of ethylene glycol.

The temperature was then increased to more than 200° C., and 48 g of theethylene glycol was removed. Then, the temperature was reduced to 150°C., and 38.4 g (0.2 mol) of trimellitic anhydride and 51.6 g (0.2 mol)of 4,4'-dicarboxydiphenyl ether were added (the OH/COOH ratio was 2.02).When the mixture was reacted at 180° to 200° C. for 3 hours, waterdistilled off, and a viscous resinous product having an acid value of 41was obtained. Then, the temperature was reduced to 100° C., and 59.4 g(0.3 mol) of 1,2,3,4-butanetetracarboxylic dianhydride and 32.4 g (0.3mol) of para-phenylene diamine were added. When the mixture was reactedat 130° to 150° C. for 30 minutes, a reddish-brown transparent resinousproduct having an acid value of 35 was obtained. Then, 35 g oftriethylene glycol was added, and the temperature was reduced to 110° C.Then, 20 g of aqueous ammonia (concentration more than 28%, industrialgrade) diluted with 100 g of water was added through the droppingfunnel, and the mixture was stirred at 100° C. for 10 minutes. Theexcess ammonia consequently volatilized, and a reddish-brown transparentwater-soluble heat-resistant insulating varnish was obtained. Thevarnish was further diluted with water to adjust the viscosity of thevarnish to 21 poises (as measured at 30° C. using a Brookfield-typeviscometer). The non-volatile content of this varnish (after drying for2 hours at 200°±2° C.) was 40.5%. The varnish had a pH of 7.0.

EXAMPLE 6

A mixture of the following products ##STR29## was prepared in the sameway as in Example 1 from 76.8 g (0.4 mol) of trimellitic anhydride, 59.2g (0.2 mol) of 3,4,3'-diphenylketonetricarboxylic anhydride, 59.4 g (0.3mol) of 4,4'-diaminodiphenylmethane and 186 g (3.0 mols) of ethyleneglycol.

Then, the temperature was increased to more than 200° C., and 106 g ofthe ethylene glycol was removed. Then, the temperature was reduced to150° C., and 118.4 g (0.4 mol) of 3,4,3'-benzophenonetricarboxylicanhydride was added (the OH/COOH ratio was 1.65). When the mixture wasreacted at 180° to 200° C. for 1 hour, water distilled off, and aviscous resinous product having an acid value of 102 was obtained. Then,the temperature was reduced to 130° C., and 234 g (1.0 mol) of1,2,3,4-butanetetracarboxylic acid and 198 g (1.0 mol) of4,4'-diaminodiphenylmethane were added. When the mixture was reacted at130° to 150° C. for 1 hour, a reddish-brown transparent resinous producthaving an acid value of 98 was obtained. Then, 150 g of ethylene glycolmonobutyl ether was added, and the temperature was reduced to 110° C.Then, 70 g of aqueous ammonia (concentration more than 28%, industrialgrade) and 50 g of triethanolamine, diluted with 100 g of water, wereadded through the dropping funnel, and the mixture was stirred for 20minutes at 100° C. to volatilize the excess ammonia. Water was furtheradded to the resulting reddish-brown transparent water-solubleheat-resistant insulating varnish to adjust the viscosity of the varnishto 15 poises (as measured at 30° C. using a Brookfield-type viscometer).The non-volatile content of this varnish (after drying for two hours at200°±2° C.) was 37.8%. The varnish had a pH of 6.8.

EXAMPLE 7

A compound of an imide ring-containing glycol (A) was prepared in thesame way as in Example 1 from 76.8 g (0.4 mol) of trimellitic anhydride,39.6 g (0.2 mol) of 4,4'-diaminodiphenylmethane and 124 g (2.0 mols) ofethylene glycol. Then, the temperature was increased to above 200° C.,and 65 g of the ethylene glycol was distilled off. The temperature wasthen reduced to 150° C., and 76.8 g (0.4 mol) of trimellitic anhydrideand 26.1 g (0.1 mol) of tris-(2-hydroxyethyl)isocyanurate were added(the OH/COOH ratio was 1.50). When the mixture was reacted at 180° to195° C. for 1 hour, water distilled off, and a viscous resinous producthaving an acid value of 95 was obtained. The temperature was thenreduced to 130° C., and 70.2 g (0.3 mol) of1,2,3,4-butanetetracarboxylic acid and 60.0 g (0.3 mol) of4,4'-diaminodiphenylether were added. When the mixture was reacted at130° to 150° C. for 2 hours, a reddish-brown transparent resinousproduct having an acid value of 76 was obtained. Then, 120 g of ethyleneglycol was added, and the temperature was reduced to 110° C.Subsequently, 25 g of aqueous ammonia (concentration more than 28%,industrial grade) and 13 g of N-methyl-diethanolamine, diluted with 100g of water, were added through the dropping funnel. When the mixture wasstirred at 100° C. for 30 minutes, the excess ammonia volatilized and areddish brown transparent water-soluble heat-resistant insulatingvarnish was obtained. The varnish was further diluted with water toadjust the viscosity of the varnish to 25 poises (as measured at 30° C.using a Brookfield-type viscometer). The non-volatile content of thisvarnish (after drying for 2 hours at 200°±2° C.) was 41.1%. The pH ofthis varnish was 6.8.

EXAMPLE 8

An imide ring-containing glycol mainly comprising a compound of thefollowing formula (F): ##STR30## was prepared in the same way as inExample 1 from 115.2 g (0.6 mol) of trimellitic anhydride, 59.4 g (0.3mol) of 4,4'-diaminodiphenylmethane and 212 g (2.0 mols) of diethyleneglycol.

Then, the temperature was increased to 245° C., and 95 g of thediethylene glycol was distilled off. The temperature was then reduced to150° C., and 76.8 g (0.4 mol) of trimellitic anhydride, 25.4 g (0.1 mol)of bis-(2-hydroxyethyl)terephthalate and 52.2 g (0.2 mol) oftris-(2-hydroxyethyl)isocyanurate were added (the OH/COOH ratio was2.00). When the mixture was reacted at 180° to 195° C. for 1 hour, waterdistilled off, and a viscous resinous product having an acid value of 77was obtained. Subsequently, the temperature was reduced to 130° C., and58.5 g (0.25 mol) of 1,2,3,4-butanetetracarboxylic acid and 49.5 g (0.25mol) of 4,4'-diaminodiphenylmethane were added. When the mixture wasreacted at 130° to 150° C. for 1 hour, water distilled off, and areddish-brown transparent resinous product having an acid value of 74was obtained. Then, 25 g of triethylene glycol monomethyl ether wasadded, and the temperature was reduced to 110° C. Then, 40 g of aqueousammonia (concentration more than 28%, industrial grade) diluted with 100g of water was added through the dropping funnel. When the mixture wasstirred at 100° C. for 30 minutes, the excess ammonia volatilized, and areddish-brown transparent water-soluble heat-resistant insulatingvarnish was obtained. Water was added to this varnish to adjust theviscosity of the varnish to 23 poises (measured at 30° C. using aBrookfield-type viscometer). The non-volatile content of this varnish(after drying for 2 hours at 200°±2° C.) was 42.0%. The varnish had a pHof 7.0.

EXAMPLE 9

An imide ring-containing glycol (A) was prepared in the same way as inExample 1 from 115.2 g (0.6 mol) of trimellitic anhydride, 59.4 g (0.3mol) of 4,4'-diaminodiphenylmethane and 186 g (3.0 mols) of ethyleneglycol. Then, the temperature was increased to above 200° C., and 117 gof the ethylene glycol was distilled off. The temperature was thenreduced to 150° C., and 96 g (0.5 mol) of trimellitic anhydride and 78.3g (0.3 mol) of tris-(2-hydroxyethyl)isocyanurate were added (the OH/COOHratio was 1.67). When the mixture was reacted at 180° to 195° C. for 1hour, water distilled off, and a viscous resinous product having an acidvalue of 98 was obtained. Subsequently, the temperature was reduced to130° C., and 117 g (0.5 mol) of 1,2,3,4-butanetetracarboxylic acid and79.2 g (0.4 mol) of 4,4' -diaminodiphenylmethane were added. When themixture was reacted at 130° to 150° C. for 2 hours, water distilled off,and a reddish-brown transparent resinous product having an acid value of86 was obtained. Then, the temperature was reduced to 110° C., and 50 gof aqueous ammonia (concentration more than 28%, industrial grade)diluted with 100 g of water was added through the dropping funnel. Whenthe mixture was stirred at 100° C. for 30 minutes, the excess ammoniavolatilized, and a reddish-brown transparent water-solubleheat-resistant insulating varnish was obtained. A solution of 5.0 g ofammonium titanium lactate in water was added, and water was furtheradded to the varnish to adjust the viscosity of the varnish to 18 poises(measured at 30° C. using a Brookfield-type viscometer). Thenon-volatile content of this varnish (after drying for 2 hours at200°±2° C.) was 40.5%. The varnish had a pH of 6.9.

EXAMPLE 10

An amide ring-containing glycol (A) was prepared in the same way as inExample 1 from 115.2 g (0.6 mol) of trimellitic anhydride, 59.4 g (0.3mol) of 4,4'-diaminodiphenylmethane, 37.2 g (0.6 mol) of ethylene glycoland 150 g of N-methyl-2-pyrrolidone. Then, the temperature was increasedto 200° C., and 100 g of the N-methyl-2-pyrrolidone was distilled off.The temperature was then reduced to 150° C., and 57.6 g (0.3 mol) oftrimellitic anhydride and 15.5 g (0.25 mol) of ethylene glycol wereadded (the OH/COOH ratio was 1.22). When the mixture was reacted at 180°to 195° C. for 1.5 hours, water distilled off, and a viscous resinousproduct having an acid value of 121 was obtained. Subsequently, thetemperature was reduced to 130° C., and 234 g (1.0 mol) of1,2,3,4-butanetetracarboxylic acid and 198 g (1.0 mol) of4,4'-diaminodiphenylmethane were added. When the mixture was reacted at130° to 150° C. for 1 hour, water distilled off, and a viscous resinousproduct having an acid value of 106 was obtained. The temperature wasthen reduced to 110° C., and 80 g of aqueous ammonia (concentration morethan 28%, industrial grade) diluted with 100 g of water was addedthrough the dropping funnel. When the mixture was stirred at 100° C. for30 minutes, the excess ammonia volatilized, and a reddish-browntransparent water-soluble heat-resistant insulating varnish wasobtained. Then, the temperature was reduced to 50° C., and a solution of30 g of ammonium zirconium lactate of the following formula ##STR31## inwater was added. Water was further added to this varnish to adjust theviscosity of the varnish to 20 poises (measured at 30° C. using aBrookfield-type viscometer). The non-volatile content of this varnish(after drying for 2 hours at 200°±2° C.) was 38.2%. The varnish had a pHof 6.7.

TEST EXAMPLES

Each of the water-soluble heat-resistant insulating varnishes obtainedin Examples 1 to 10 above was coated on a 1.0 mm-thick soft copper wire(corresponding to AWG 18 Copper Wire) using a die at a rate of 6.5 m/minand baked in a vertical-type baking furnace having a length of 3.0 m ata temperature of 400° C. The characteristics of the insulated wiresobtained are shown in Table 1.

For comparison, a polyesterimide resin varnish prepared by a customarymethod from dimethyl terephthalate, ethylene glycol,tris-(2-hydroxyethyl)isocyanurate, trimellitic anhydride and4,4'-diaminodiphenylmethane as predominant raw materials using a solventconsisting mainly of cresol was coated and baked in the same way asdescribed above, and the characteristics of the resulting insulatedwires are also shown in Table 1.

The tests for the characteristics of the insulated wire were conductedin accordance with JCS-333 (1970) (Class H, polyesterimide copperwires).

                                      TABLE 1                                     __________________________________________________________________________    Characteristics of Insulated Wires                                                                                                     Compari-                              1   2   3   4   5   6   7   8   9   10  son                  __________________________________________________________________________    Wire Structure:                                                                Enameled Wire Diameter (mm)                                                                   1.075                                                                             1.073                                                                             1.076                                                                             1.071                                                                             1.073                                                                             1.070                                                                             1.073                                                                             1.075                                                                             1.073                                                                             1.075                                                                             1.075                 Bare Wire Diameter (mm)                                                                       0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                                                                             0.995                 Film Thickness (mm)                                                                           0.040                                                                             0.039                                                                             0.041                                                                             0.038                                                                             0.039                                                                             0.038                                                                             0.039                                                                             0.040                                                                             0.039                                                                             0.040                                                                             0.040                Windability:                                                                   Self-Diameter (normal                                                                         Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                  condition)                                                                    Self-Diameter (at 20%                                                                         Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                  stretch)                                                                      After Heating (24 hrs. at                                                                     2d, 2d, 1d, 1d, 2d, 2d, 2d, 1d, 1d, 2d, 2d,                   200° C.  Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                 Abrasion Resistance (cycles)                                                                    87 109  81  76  97 102  70  68  98  79  45                  (under a load of 700 g)                                                       Cut-Through Temperature (° C.)                                                          448 425 436 410 426 441 428 421 436 448 425                  (2 kg load, 2° C./min.                                                 Heat Shock Resistance                                                                          2d, 1d, 1d, 2d, 1d, 1d, 2d, 2d, 1d, 1d, 2d,                  (200° C. × 2 hrs.)                                                                Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                 Dielectric Breakdown (kv)                                                                      13.9                                                                              15.4                                                                              14.8                                                                              15.0                                                                              13.6                                                                              14.2                                                                              15.0                                                                              14.6                                                                              15.3                                                                              15.1                                                                              13.2                 Chemical Resistance (dipped for                                               24 hrs at room temperature)                                                    Pencil Hardness (at normal                                                                    5H  5H  5H  5H  5H  5H  5H  5H  5H  5H  5H                    conditions)                                                                   Pencil Hardness (after                                                                        4H  5H  5H  5H  4H  5H  5H  5H  5H  5H  4H                    dipping in 5% NaOH)                                                           Pencil Hardness (after                                                                        5H  5H  5H  5H  5H  5H  5H  5H  5H  5H  5H                    dipping in H.sub.2 SO.sub.4 (specific                                         gravity: 1.2))                                                               Crazing in Water*                                                                              0/5 0/5 0/5 0/5 0/5 0/5 0/5 0/5 0/5 0/5 4/5                  (at 3% stretch)                                                               __________________________________________________________________________     *No. of samples crazing/no. of samples tested.                           

As demonstrated above, baked films obtained from the insulating varnishof this invention have superior crazing characteristics, wear resistanceand heat resistance as compared with the conventional solvent-typeesterimide resin varnishes in which cresol is a main solvent. Sincewater is used as a medium in the varnish of this invention, atmosphericpollution as a result of volatilization of the solvent or toxic gasesduring baking is not caused, and the working environment is extremelysafe. In addition, the varnish of this invention scarcely gives off anyoffensive odor, and there is almost no danger of fire or explosion.Furthermore, the use of water as a medium renders the varnish of thisinvention far less expensive than the conventional solvent-typeesterimide resin varnishes, and the commercial significance of thisinvention is great.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A coated article comprising a metal support and abaked layer of a water-soluble heat-resistant insulating varnishcontaining a resin comprising ester groups and imide rings in themolecule dissolved in water using a volatilizable basic compound, saidresin comprising the reaction product of(A) a carboxyl-containingpolyesterimide resin having an acid value of about 30 to 150 obtained byreacting (a) a polyhydric alcohol component comprising at least oneorganic polyhydric alcohol and containing about 10 to 60 mol % of animide ring-containing glycol of the general formula(I): ##STR32##wherein R₁ is a trivalent aromatic group, R₂ is a divalent organicgroup, and n is an integer of 1 to 3, with (b) a polycarboxylic acidcomponent comprising at least one trivalent or divalent organiccarboxylic acid or the anhydride thereof, about 30 to 100 mol % of whichcomprises an aromatic tricarboxylic acid or the anhydride thereof sothat the equivalent ratio (OH/COOH) between the polyhydric alcoholcomponent and the polycarboxylic acid component is about 1.0 to 2.0; (B)1,2,3,4-butanetetracarboxylic acid or an imide-forming derivativethereof, and (C) an organic diamine.
 2. The coated article of claim 1,wherein said varnish further contains a water-soluble organic metalcompound as a curing agent.
 3. The coated articles of claim 2, whereinsaid organic metal compound is titanium ammonium lactate, titaniumlactate or zirconium ammonium lactate.
 4. The coated articles of claim3, wherein the amount of said organic metal compound is up to about 10parts by weight per 100 parts by weight of said resin comprising thereaction product of (A), (B) and (C).
 5. The coated articles of claim 1,wherein up to about 30 mol % of said aromatic tricarboxylic acid or theanhydride thereof of said polycarboxylic acid component is replaced byan aromatic tetracarboxylic acid or the anhydride thereof.
 6. The coatedarticles of claim 1, wherein the total amount of said1,2,3,4-butanetetracarboxylic acid or the imide-forming derivativethereof (B) and said organic diamine (C) is about 20 to 200 parts byweight per 100 parts by weight of said polyesterimide resin (A).
 7. Thecoated articles of claim 6, wherein said total amount is 30 to 150 partsby weight per 100 parts by weight of said polyesterimide resin (A). 8.The coated articles of claim 1, wherein the equivalent ratio of said1,2,3,4-butanetetracarboxylic acid or the imide-forming derivativethereof (B) to said organic diamine (C) is about 0.5 to
 2. 9. The coatedarticles of claim 8, wherein said equivalent ratio is 0.8 to 1.3. 10.The coated articles of claim 1, wherein said volatilizable basiccompound is selected from the group consisting of ammonia, aqueousammonia, trialkylamines, N-alkyldiethanolamines,N,N-dialkylethanolamines, monoethanolamine, diethanolamine andtriethanolamine.
 11. The coated articles of claim 1, wherein up to about30% by weight of said water is replaced by a water-soluble high-boilingsolvent.
 12. The coated article of claim 1, wherein said imidering-containing glycol of formula (I) is prepared by reacting about 2mols of an aromatic tricarboxylic acid anhydride with 1 mol of anorganic diamine in a glycol selected from the group consisting ofethylene glycol, diethylene glycol and triethylene glycol.
 13. Thecoated articles of claim 1, wherein said polyhydric alcohol is ethyleneglycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol,1,10-decanediol, diethylene glycol, dipropylene glycol, triethyleneglycol, 4,4'-dihydroxymethyldiphenyl, 4,4'-dihydroxyethyldiphenyl,4,4'-dihydroxymethyldiphenylmethane, 4,4'-dihydroxyethyldiphenylmethane,4,4'-dihydroxymethyldiphenyl ether, 4,4'-dihydroxyethyldiphenyl ester,4,4'-dihydroxymethyldiphenyl sulfide, 4,4'-dihydroxyethyldiphenylsulfide, 4,4'-dihydroxymethyldiphenyl sulfone,4,4'-dihydroxyethyldiphenyl sulfone, 4,4'-dihydroxymethyldiphenylketone, 4,4'-dihydroxyethyldiphenyl ketone,4,4'-dihydroxymethyldiphenylpropane, 4,4'-dihydroxyethyldiphenylpropane,bis-(2-hydroxyethyl)terephthalate, bis-(2-hydroxyethyl)isophthalate,bis-(2-hydroxyethyl)phthalate, glycerol, trimethylol propane,1,2,6-hexanetriol, 3-methyl-1,3,5-hexanetriol,tris-(2-hydroxyethyl)isocyanurate, pentaerythritol, or mixtures of theseorganic polyhydric alcohols.
 14. The coated articles of claim 1, whereinsaid aromatic tricarboxylic acid or the anhydride thereof is representedby formula (IV) or (V), respectively ##STR33## wherein R₁ is a trivalentaromatic group selected from the group consisting of ##STR34## whereinR₃ is selected from the groups consisting of ##STR35##
 15. The coatedarticle of claim 1, wherein said aromatic tricarboxylic acid or theanhydride thereof is trimellitic acid or the anhydride thereof, trimesicacid or the anhydride thereof, 3,4,3'- or 3,4,4'-diphenyltricarboxylicacid or the anhydride thereof, 3,4,3'- or3,4,4'-diphenylmethanetricarboxylic acid or the anhydride thereof,3,4,3'- or 3,4,4'-diphenylether tricarboxylic acid or the anhydridethereof, 3,4,3'- or 3,4,4'-diphenylsulfidetricarboxylic acid or theanhydride thereof, 3,4,3'- or 3,4,4'-diphenylsulfonetricarboxylic acidor the anhydride thereof or the anhydride thereof 3,4,3'- or3,4,4'-diphenylketonetricarboxylic acid or the anhydride thereof,3,4,3'- or 3,4,4'-diphenylpropanetricarboxylic acid or the anhydridethereof, or mixtures thereof.
 16. The coated articles of claim 1,wherein said divalent organic carboxylic acid or the anhydride thereofis an organic dicarboxylic acid or the anhydride thereof represented bygeneral formula (VI) or (VII), respectively

    HOOC--R.sub.5 --COOH                                       (VI)

or ##STR36## in which R₅ is a divalent organic group selected from thegroup consisting of

    --CH.sub.2).sub.n.sbsb.2

in which n₂ is an integer of 1 to 8, ##STR37## in which R₃ is selectedfrom the group consisting of ##STR38##
 17. The coated article of claim16, wherein said divalent organic carboxylic acid or the anhydridethereof is succinic acid, succinic anhydride, adipic acid, malonic acid,sebacic acid, phthalic acid, phthalic anhydride, isophthalic acid,terephthalic acid, naphthalene dicarboxylic acid having the formula##STR39## dicarboxydiphenyl having the formula ##STR40##dicarboxydiphenylmethane, dicarboxydiphenyl ether, dicarboxydiphenylsulfide, dicarboxydiphenyl sulfone, dicarboxydiphenyl ketone,dicarboxydiphenyl propane having the formula ##STR41## wherein Rrepresents a methylene group, an oxygen atom, a sulfur atom, an --SO₂group, ##STR42## group or mixtures thereof.
 18. The coated articles ofclaim 1, wherein said 1,2,3,4-butanetetracarboxylic acid or theimide-forming derivative thereof is selected from the group consistingof 1,2,3,4-butanetetracarboxylic acid, 1,2,3,4-butanetetracarboxylicmonoanhydride, 1,2,3,4-butanetetracarboxylic dianhydride, and dimethyl1,2,3,4-butanetetracarboxylate.
 19. The coated articles of claim 1,wherein said organic diamine is represented by the formula

    H.sub.2 N--R.sub.2 --NH.sub.2

in which R₂ is selected from the group consisting of

    --CH.sub.2)n.sub.1

wherein n₁ is an integer of 1 to 6, ##STR43## wherein R'₃ is selectedfrom the group consisting of ##STR44## and R₄ is selected from the groupconsisting of a hydrogen atom, an alkoxy group, an alkyl group and ahalogen atom.
 20. The coated articles of claim 12, wherein said aromatictricarboxylic acid or the anhydride thereof is represented by generalformula (IV) or (V), respectively ##STR45## wherein R₁ is a trivalentaromatic group selected from the group consisting of ##STR46## whereinR₃ is selected from the group consisting of ##STR47##
 21. The coatedarticle of claim 20 wherein said aromatic tricarboxylic acid or theanhydride thereof is trimellitic acid or the anhydride thereof,hemimellitic acid or the anhydride thereof, trimesic acid or theanhydride thereof, 3,4,3'- or 3,4,4'-diphenyltricarboxylic acid or theanhydride thereof, 3,4,3'- or 3,4,4'-diphenylmethanetricarboxylic acidor the anhydride thereof, 3,4,3'- or 3,4,4'-diphenylether tricarboxylicacid or the anhydride thereof, 3,4,3'- or3,4,4'-diphenylsulfidetricarboxylic acid or the anhydride thereof,3,4,3'- or 3,4,4'-diphenylsulfonetricarboxylic acid or the anhydridethereof, 3,4,3'- or 3,4,3'-diphenylketonetricarboxylic acid or theanhydride thereof, 3,4,3'- or 3,4,4'-diphenylpropanetricarboxylic acidor the anhydride thereof, and mixtures thereof.
 22. The coated articlesof claim 12, wherein said organic diamine is represented by the formula

    H.sub.2 N--R.sub.2 --NH.sub.2

in which R₂ is selected from the group consisting of

    --CH.sub.2)n.sub.1

wherein n₁ is an integer of 1 to 6, ##STR48## wherein R'₃ is selectedfrom the group consisting of ##STR49## and R₄ is selected from the groupconsisting of a hydrogen atom, an alkoxy group, an alkyl group and ahalogen atom.
 23. The coated articles of claim 1, wherein the equivalentratio (OH/COOH) between the polyhydric alcohol component and thepolycarboxylic acid component is 1.15 to 1.95.
 24. The coated articlesof claim 1, wherein the acid value of the carboxyl-containingpolyesterimide resin is 50 to
 120. 25. The coated articles of claim 1,wherein the reaction product of (A) a carboxyl-containing polyesterimideresin, (B) 1,2,3,4-butanetetracarboxylic acid or an imide-formingderivative thereof and (C) an organic diamine has an acid value in therange of from about 30 to
 150. 26. The coated articles of claim 1,wherein said resin is dissolved in a volatilizable basic compound in anamount of about 0.3 to 3 equivalents based on the residual carboxylgroups in said resin.
 27. The coated articles of claim 1, wherein thevarnish has a pH of from about 5 to
 9. 28. The coated article of claim1, wherein said support is an electrical conductor.
 29. The coatedarticle of claim 28, wherein said electrical conductor is a wire. 30.The coated article of claim 29, wherein said wire is a soft copper wire.31. The coated article of claim 1, wherein said coated article comprisesan electric wire or cable as said support having thereon at least twoelectrically insulating layers, one of which comprises said baked layerof said water-soluble heat-resistant insulating varnish of claim 1 as anovercoat or a primer.
 32. The coated article of claim 1, wherein saidbaked layer is based at a temperature above about 200° C.
 33. The coatedarticle of claim 32, wherein said temperature is 300° to 500° C.
 34. Thecoated article of claim 12, wherein said aromatic tricarboxylic acidanhydride is represented by the general formula (II) ##STR50## in whichR₁ is selected from the group consisting of ##STR51## wherein R₃ isselected from the group consisting of ##STR52##
 35. The coated articleof claim 34, wherein said aromatic tricarboxylic acid anhydride isselected from the group consisting of trimellitic anhydride,hemimellitic anhydride, 3,4,3'-or 3,4,4'-diphenyltricarboxylicanhydride, 3,4,3'-or 3,4,4'-diphenylmethanetricarboxylic anhydride,3,4,3'-or 3,4,4'-diphenylethertricarboxylic anhydride, 3,4,3'-or3,4,4'-diphenylsulfidetricarboxylic anhydride, 3,4,3'-or3,4,4'-diphenylsulfonetricarboxylic anhydride, 3,4,3'-or3,4,4'-diphenylketonetricarboxylic anhydride, 3,4,3'-or3,4,4'-diphenylpropanetricarboxylic anhydride, and mixtures of theseanhydrides.
 36. The coated article of claim 1, wherein in the amount ofthe imide ring-containing glycol of the general formula (I) among thetotal amount of the (A) component is about 20 to 70% by weight.
 37. Thecoated article of claim 36, wherein the amount of the imidering-containing glycol of the general formula (I) among the total amountof the (A) component is 30 to 60% by weight.
 38. The coated article ofclaim 4, wherein the amount of said organic metal compound is 0.1 to 50parts by weight per 100 parts by weight of said resin comprising thereaction product of (A), (B) and (C).